The CAA’s board is expected to approve plans for the preliminary work, with prime minister Boris Johnson having apparently changed his stance on the airport’s expansion.
Johnson had previously said he would lie down in front of the bulldozers to oppose a third runway, but has since hinted he has changed his views.
Heathrow must still receive full planning approval for its proposals and faces a lengthy court battle with objectors.
One group, Heathrow Hub, argues that an existing runway could be extended for take-off and landing and is demanding a full review of the cost.
